JP2004254283A - Automatic gain control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic gain control apparatus which secures a required linearity from a weak electric field to a strong electric field and can converge gain control at a high speed. <P>SOLUTION: An automatic gain control apparatus 20 is composed of an input terminal 21, an input coupler 22 for taking out a part of an input signal, an attenuator 23 for switching a passing state and an attenuating state according to a logic signal, a variable gain amplifier 25 capable of continuously controlling a gain under a control voltage, an output coupler 26 for taking out a part of an output from the variable gain amplifier 25, an output terminal 28, a first control part 24 for switching the state of the attenuator 23 from the passing state to the attenuating state when the input of the automatic gain control apparatus 20 exceeds a specified threshold, and a second control part 27 for controlling the gain of the variable gain amplifier 25 to fix the output of the automatic gain control apparatus 20. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an automatic gain control device.

  Conventionally, a receiving device using an automatic gain control device has been proposed (for example, see Patent Document 1).

  In this receiving apparatus, a first attenuator provided between a front end or a high-frequency amplifier and a mixer and a preceding stage of an RSSI circuit that generates a received signal strength detection signal (RSSI: Received Signal Strength Indication) from a received signal. A second attenuator provided to adjust the input signal level and the RSSI output signal are compared with two threshold values. If the two signals are other than the threshold values, the attenuation of the second attenuator is adjusted first, and after the adjustment, the first attenuator is adjusted. And a reception level control unit for adjusting the amount of attenuation of the second attenuator, so that a wide range of signal levels can be received while preventing saturation of each circuit, and an accurate reception level can be transmitted to the system in a timely manner. I have to.

  FIG. 17 is a block diagram showing a basic configuration example of a conventional automatic gain control device. As shown in FIG. 17, the automatic gain control device 10 includes an input terminal 11, a variable gain amplifier 12 for continuously controlling the gain by a control voltage, a coupler 13 for extracting a part of the output of the variable gain amplifier 12, and an output terminal 14. And a control unit 15 for controlling the gain of the variable gain amplifier 12 so that the output of the automatic gain control device 10 becomes constant.

  Here, the control unit 15 includes a detector 151, a reference voltage source 152, and an error amplifier 153.

A part of the output of the variable gain amplifier 12 obtained by the coupler 13 is converted into a DC voltage signal by the detector 151, and is output by the error amplifier 153 so that the voltage value matches the reference voltage value of the reference voltage source 152. The gain of the variable gain amplifier 12 is controlled, so that the automatic gain control device 10 can obtain a constant output signal level.
JP-A-2002-94408 (Claim 1)

  However, in a conventional receiving apparatus, although saturation of each circuit is prevented, a wide range of signal levels is received, and an accurate reception level is transmitted to the system in a timely manner. In a digital communication system that aims at high-speed data transmission by employing a modulation method such as an orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing) method, there is a problem that high linearity and high-speed response required for a receiving device are not considered. .

  For example, in a digital communication system intended for high-speed data transmission, a base station and a terminal are used in close proximity of 1 m or less, as in a high-speed wireless LAN system, or a shielding system existing between the base station and the terminal is used. In some cases, the propagation loss increases depending on the object, and only a very weak reception signal level can be obtained. For this reason, an automatic gain control device applied to the receiving unit is required to have a wide dynamic range that can support a wide range of received signal levels from a weak electric field to a strong electric field.

  For example, in a wireless LAN system, a preamble signal having a known pattern is added to the head of a transmitted data burst signal, and the automatic gain control device controls the gain based on the reception level of the preamble signal. If the preamble signal is long, the data transmission throughput is reduced. Therefore, an automatic gain control device is required to have a high-speed response characteristic in which the gain converges with high accuracy even with a short preamble signal.

  In order to realize these requirements with the conventional automatic gain device, there are the following problems.

  Among components constituting a receiving circuit, a mixer or a variable gain amplifier for converting a radio frequency to an intermediate frequency generally has a high noise figure. In order to reduce the noise figure of the entire receiving circuit using these components and to obtain a desired sensitivity even in a weak electric field, as shown in FIG. 18, a high gain must be provided before the component having a high noise figure. Therefore, it is necessary to increase the denominator of the influence term of these components having a high noise figure to reduce the influence on the noise figure of the entire circuit. However, if the gain of the former stage of the circuit is high, there is a problem that components in the latter stage become excessively input in a strong electric field and the signal is distorted.

  In addition, the gain of the variable gain amplifier must be set to the maximum gain in the initial state so that a weak signal is not missed. However, when a strong electric field input is received, the variable gain amplifier saturates and the control voltage is reduced. , The change in the output signal level becomes smaller. For this reason, it takes time to converge to a desired output level, and there is a problem that it is difficult to achieve both linearity from a weak electric field to a strong electric field and high-speed response characteristics.

  The present invention has been made in view of the above, and an object of the present invention is to provide an automatic gain control device that can secure required linearity from a weak electric field to a strong electric field and can converge gain control at high speed. I do.

  An automatic gain control device according to the present invention is an automatic gain control device that performs gain control so that an output signal level becomes constant in accordance with an input received signal level, wherein the gain for discretely changing a gain for amplifying the received signal is provided. Switching means; gain control means for continuously controlling the gain for amplifying the received signal output by the gain switching means; and detecting a received signal level at an input stage of the gain switching means, wherein the level is equal to or higher than a predetermined threshold. A first control unit that switches the gain of the gain switching unit in a direction in which the gain is reduced, and a second control unit that controls the gain of the gain control unit so that the output signal level of the gain control unit is constant. The configuration provided is adopted.

  According to this configuration, since the gain control is performed by combining the discrete gain switching and the continuous gain control for the received signal from the weak electric field to the strong electric field, the required linearity is obtained from the weak electric field to the strong electric field. And gain control can be converged at high speed.

  In the automatic gain control device according to the present invention, the first control means may have a hysteresis characteristic based on different thresholds depending on whether the variation of the received signal level is increasing or decreasing. A configuration for switching the gain of the gain switching means is adopted.

  According to this configuration, the gain control is performed on the received signal from the weak electric field to the strong electric field by combining the gain switching with the discrete and hysteresis characteristics and the continuous gain control. The linearity can be ensured, the gain control can be converged at high speed, and the output stable with respect to the level fluctuation of the received signal can be ensured.

  The automatic gain control device according to the present invention employs a configuration in which the first and second control means switch between gain change and gain fixation by a timing signal input from the outside to perform control.

  According to this configuration, for a received signal from a weak electric field to a strong electric field, gain control is performed by combining discrete gain switching and continuous gain control, and a period during which the gain is changed and a period during which the gain is fixed are set. Since the switching is performed, required linearity can be secured in the gain characteristic of the amplifier, gain control can be converged at high speed, and a stable output can be secured with respect to the level fluctuation of the received signal.

  The automatic gain control device of the present invention employs a configuration in which the first control means has a delay element disposed between a portion for detecting the reception signal level and an input stage of the gain switching means.

  According to this configuration, by utilizing the delay of the received signal by the delay element, discrete gain switching can be performed before the received signal is transmitted, and gain control can be converged more quickly.

  The automatic gain control device of the present invention employs a configuration in which the delay element has a frequency selection characteristic.

  According to this configuration, by providing the filter function to the delay element, the number of components can be reduced, and the receiving circuit can be made cheaper and smaller.

  According to the present invention, required linearity can be secured from a weak electric field to a strong electric field, and gain control can be converged at high speed.

  The gist of the present invention is to perform a gain control by combining a discrete gain switching and a continuous gain control on a received signal ranging from a weak electric field to a strong electric field, to secure required linearity in the gain characteristic of the amplifier, And to enable gain control to converge at high speed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of an automatic gain control device 20 according to Embodiment 1 of the present invention.

  The automatic gain control device 20 mainly includes an input terminal 21, an input coupler 22, an attenuator 23, a first control unit 24, a variable gain amplifier 25, an output coupler 26, a second control unit 27, and an output terminal 28. You.

  The input coupler 22 extracts a part of the received signal input from the input terminal 21 and outputs it to the first controller 24.

  The attenuator 23 receives, from the first controller 24, an attenuation path T1 that attenuates an input signal by a predetermined amount of attenuation, a passage path T2 that allows the input signal to pass through without attenuation, and attenuation paths T1 and T2. And a switch SW that switches according to the logical signal to be received, and attenuates the reception signal input from the input coupler 22 by the attenuation path T1 or passes the reception signal by the passage path T2 to output to the variable gain amplifier 25.

  The first control unit 24 includes a detector 241, a reference voltage source 242, and a comparator 243. The detector 241 converts a received signal input from the input coupler 22 into a DC voltage signal. The comparator 243 compares the reference voltage value of the voltage source 242 and outputs a logic signal to the attenuator 23 for switching the switch SW of the attenuator 23 to the attenuation path T1 or the passage path T2 based on the comparison result.

  The variable gain amplifier 25 can continuously control the gain by the gain control signal input from the second control unit 27, amplifies the reception signal input from the attenuator 23 by the set gain, and outputs the output coupler 26. Output to

  The output coupler 26 extracts a part of the amplified reception signal input from the variable gain amplifier 25 and outputs it to the second control unit 27.

  The second control unit 27 includes a detector 271, a reference voltage source 272, and an error amplifier 273. The detector 271 converts the amplified reception signal input from the output coupler 26 into a DC voltage signal. The error amplifier 273 controls the gain of the variable gain amplifier 25 so that the reference voltage and the reference voltage value of the reference voltage source 272 match.

  In the above configuration example, the gain switching means according to claim 1 is used as the attenuator 23. However, since the function required of the gain switching means is to discretely switch the gain, for example, the gain can be switched. An amplifier may be applied.

  In the above configuration example, the gain control means according to claim 1 is a variable gain amplifier 25, but the function required for the gain control means is within the optimum input range of the circuit to which the output of the automatic gain control device is connected. Therefore, for example, a digital attenuator whose minimum resolution is equal to or less than the optimum input range may be applied.

  In the above configuration example, the functions of the first control unit 24 and the second control unit 27 are realized by analog control, but they may be realized by digital control.

  In the above configuration example, the second control unit 27 controls the gain of the variable gain amplifier 25 by feeding back the output signal of the variable gain amplifier 25. For example, the second control unit 27 connects the output coupler 26 to the attenuator 23 and the variable gain amplifier 25. , The input level of the variable gain amplifier 25 is detected, and the gain of the variable gain amplifier 25 may be controlled so as to obtain a gain different from the desired output level.

  Next, the operation of each unit when the strong electric field is input in the automatic gain control device 20 having the above configuration will be described with reference to the block diagram shown in FIG. 2 and the timing chart of each unit signal shown in FIG.

  3A shows a received signal input to the input terminal 21, FIG. 3B shows an output signal of an output unit (A in FIG. 2) of the first control unit 24, and FIG. The output signal of the output section (B in FIG. 2), and FIG. 2D shows the operation state of the output signal output from the output terminal 28.

  It is assumed that the switch SW in the attenuator 23 has been switched to the passing path T2 in the initial state.

  In the automatic gain control device 20 of FIG. 2, when the reception signal of FIG. 3A is input to the input terminal 21, a part of the signal is extracted by the input coupler 22 and output to the first control unit 24.

  In the first control unit 24, a DC voltage value obtained by DC-converting the received signal input from the input coupler 22 is compared with a reference voltage value (threshold) of the reference voltage source 242 by the comparator 243. In this case, since the voltage value of the received signal in FIG. 3A exceeds the threshold value indicating the reference voltage value, the comparator 243 determines that the signal path of the attenuator 23 is a logical signal for switching the signal path from the passing path T2 to the attenuation path T1. The "High" signal shown in FIG. 3B is output to the attenuator 23 (the output of A in FIG. 2).

  In the attenuator 23, the switch SW is switched from the passing path T2 in the initial state to the attenuation path T1 at the switching timing shown in FIG. 3B by the logic signal of FIG. 3B input from the comparator 243 of the first control unit 24. As a result, the output signal (B in FIG. 2) output from the attenuator 23 is a signal attenuated by the attenuation path T1 as shown in FIG. 3C.

  In the variable gain amplifier 25, when the received signal is input to the automatic gain control device 20, that is, in a state where the switch SW in the attenuator 23 is switched to the passing path T2, the rising of the received signal causes a sharp rise in FIG. As shown in (d), the output signal reaches the temporary saturation level.

  However, immediately after that, the switch SW in the attenuator 23 is immediately switched to the attenuation path T1 by the operation of the first control unit 24, and the received signal is attenuated. Therefore, the output signal of the variable gain amplifier 25 is shown in FIG. Is quickly converged to the desired output level shown in FIG.

  Next, the operation of each unit when the weak electric field is input in the automatic gain control device 20 having the above configuration will be described with reference to the block diagram shown in FIG. 4 and the timing chart of each unit signal shown in FIG.

  Here, the monitoring points A and B of each signal in the automatic gain control device 20 shown in FIG. 4 are the same as the monitoring points A and B of each signal shown in FIG. 2 and are shown in FIGS. Are the same as those shown in FIGS. 3 (a) to 3 (d).

  It is also assumed that the switch SW in the attenuator 23 has been switched to the passing path T2 in the initial state.

  In the automatic gain control device 20 of FIG. 4, when the reception signal of FIG. 5A is input to the input terminal 21, a part of the signal is extracted by the input coupler 22 and input to the first control unit 24.

  In the first control unit 24, a DC voltage value obtained by DC-converting the received signal input from the input coupler 22 is compared with a reference voltage value (threshold) of the reference voltage source 242 by the comparator 243. In this case, since the voltage value of the received signal in FIG. 5A does not exceed the threshold value indicating the reference voltage value, the comparator 243 uses a logic signal for maintaining the signal path of the attenuator 23 in the passing path T2 as shown in FIG. The output of the “Low” signal shown in (b) to the attenuator 23 is continued (the output of A in FIG. 4).

  In the attenuator 23, the connection of the passage T2 of the switch SW is maintained by the logic signal of FIG. 5B input from the comparator 243 of the first control unit 24. As a result, as the output signal (B in FIG. 4) output from the attenuator 23, an unattenuated signal that has passed through the passing path T2 is output as shown in FIG. 5C.

  In the variable gain amplifier 25, the output signal temporarily exceeds the desired output level, as shown in FIG. 5D, at the beginning of the input of the received signal to the automatic gain control device 20, that is, due to the steep rise of the received signal.

  However, the output signal of the variable gain amplifier 25 is quickly converged to the desired output level shown in FIG. 5D by the operation of the second control unit 27. That is, the operating point of the variable gain amplifier 25 is within the linear region from the reception start point, and the output level appearing at the output terminal 28 by the second control unit 27 converges to the desired output level at high speed.

  FIG. 6 is a diagram showing an example of a conventional automatic gain control device and an input electric field level and a dynamic range of the automatic gain control device 20 according to the first embodiment.

  In FIG. 6, when the input electric field level is -90 dBm to -20 dBm, in the conventional automatic gain control device, the required dynamic range is 70 dB, and it is necessary to maintain linearity up to the maximum input level = -20 dBm.

  In the automatic gain control device 20 according to the first embodiment of the present invention, the loss when switching to the passing path T2 of the attenuator 23 is 0 dB, the loss when switching to the attenuation path T1 is 30 dB, and the threshold for switching between passing and attenuation is Assuming -50 dBm, the dynamic range of the variable gain amplifier 25 can be compressed to 40 dB, and the maximum input level can be reduced to -50 dBm.

  Therefore, even if variable gain amplifiers having the same characteristics are used, the maximum input level can be reduced by 30 dB in the above configuration example by applying the present invention, so that the saturation of the variable gain amplifier 25 in the initial reception state can be avoided and high speed can be achieved. The gain can be converged, and the noise figure of the entire circuit can be reduced by increasing the gain of the circuit preceding the automatic gain control device 20.

  As described above, according to the automatic gain control device 20 of the first embodiment, there is provided an automatic gain control device capable of securing required linearity from a weak electric field to a strong electric field and capable of converging response characteristics at high speed. can do.

  FIG. 7 shows a configuration example of a receiving circuit 70 to which the automatic gain control device 20 according to the first embodiment is applied. In addition, the same reference numerals are given to the portions corresponding to FIG. 1 in the respective components in FIG.

  7, a receiving circuit 70 includes an antenna 71, a high-frequency band-pass filter 72, a low-noise amplifier 73, a mixer 74, a low-pass filter 75 for suppressing local signals, a first interstage amplifier 76, and an intermediate frequency band-pass filter 77. , An input coupler 22, an attenuator 23, a first controller 24, a variable gain amplifier 25, an output coupler 26, a second controller 27, a second interstage amplifier 78, and a quadrature demodulator 79. Is demodulated into a digital signal by a baseband processing unit (not shown).

  Thus, by applying the automatic gain control device 20 to the receiving circuit 70, a receiving device having high linearity and high-speed response can be provided.

  In order to reduce the influence of the adjacent channel interference wave, it is desirable that the input coupler 22 be disposed after the intermediate frequency band-pass filter 77.

  Further, components constituting a receiving circuit may be arranged between the input coupler 22, the attenuator 23, the variable gain amplifier 25, and the output coupler 26 constituting the automatic gain control device 20.

(Embodiment 2)
FIG. 8 is a block diagram showing a configuration of an automatic gain control device 80 according to Embodiment 2 of the present invention, wherein the same components as those shown in FIG.

  A feature of the present embodiment is that it has an attenuator that discretely switches a plurality of attenuation amounts, and a first control unit that appropriately switches the attenuation amount of the attenuator according to a level change of a received signal.

  The automatic gain control device 80 mainly includes an input terminal 21, an input coupler 22, an attenuator 81, a first control unit 82, a variable gain amplifier 25, an output coupler 26, a second control unit 27, and an output terminal 28. You. The description of the configuration of the input coupler 22, the variable gain amplifier 25, the output coupler 26, and the second control unit 27 is omitted because it is the same as that of the first embodiment.

  The attenuator 81 includes an attenuation path T1 that attenuates an input signal by a predetermined amount of attenuation, an attenuation path T2 that attenuates an input signal by a predetermined amount of attenuation, a passage path T3 that allows an input signal to pass through without attenuation, and an attenuation path. A switch SW for switching between T1 and T2 and a passage path T3 according to a logical signal input from the first control unit 82, and attenuating a reception signal input from the input coupler 22 by a plurality of attenuation paths T1 and T2. Or through the passing path T2 and output to the variable gain amplifier 25.

  It is assumed that the attenuation amount of the attenuation path T2 is larger than the attenuation amount of the attenuation path T1.

  The first control unit 82 includes a detector 821, a reference voltage source 822, a comparator 823, an interstage amplifier 824, and a comparator 825, and converts a received signal input from the input coupler 22 into a DC voltage signal by the detector 821. Then, the DC voltage value is compared with the reference voltage value of the reference voltage source 822 by the comparator 823, and the DC voltage value amplified by the inter-stage amplifier 824 is compared by the comparator 825, and based on each comparison result, A logic signal for switching the switch SW of the attenuator 81 to the attenuation paths T1 and T2 or the passage path T3 is output to the attenuator 81.

  In the above configuration example, the gain switching means according to claim 1 is used as the attenuator 81. However, since the function required of the gain switching means is to discretely switch the gain, for example, an amplifier capable of switching the gain is used. May be applied. Further, in the above configuration example, the configuration in which the function of the first control unit 82 is realized by analog control has been described, but it may be realized by digital control.

  FIG. 9 is a diagram illustrating an example of a conventional automatic gain control device and an input electric field level and a dynamic range of the automatic gain control device 80 according to the second embodiment.

  In FIG. 9, when the input electric field level is -90 dBm to -20 dBm, in the conventional automatic gain control device, the required dynamic range is 70 dB, and it is necessary to maintain the linearity up to the maximum input level = -20 dBm.

  As described above, according to the automatic gain control device 80 according to the second embodiment, the loss of the passing path T3 of the attenuator 81 is 0 dB, the losses of the attenuation paths T1 and T2 are 20 dB and 40 dB, and the threshold for switching the passing / attenuation is Assuming -60 dBm and -40 dBm, the dynamic range of the variable gain amplifier 25 can be compressed to 30 dB and the maximum input level can be reduced to -60 dBm, so that faster gain convergence and a reduction in the noise figure of the entire circuit are realized. can do.

(Embodiment 3)
FIG. 10 is a block diagram showing a configuration of an automatic gain control device 100 according to Embodiment 3 of the present invention, and the same components as those shown in FIG.

  A feature of the present embodiment is that it has a first control unit that switches the attenuation of the attenuator discretely and with a hysteresis characteristic according to the level fluctuation tendency of the received signal.

  The automatic gain control device 100 mainly includes an input terminal 21, an input coupler 22, an attenuator 23, a first control unit 101, a variable gain amplifier 25, an output coupler 26, a second control unit 27, and an output terminal 28. You. The description of the configuration of the input coupler 22, the attenuator 23, the variable gain amplifier 25, the output coupler 26, and the second control unit 27 is omitted since it is the same as that of the first embodiment.

  The first control unit 101 includes a detector 1011, a reference voltage source 1012, and a comparator 1013 having a hysteresis characteristic, and converts a received signal input from the input coupler 22 into a DC voltage signal by the detector 1011. A change in the voltage value and an ascending threshold value and a descending threshold value based on the reference voltage value of the reference voltage source 1012 are compared by the comparator 1013, and based on the comparison result, the switch SW of the attenuator 23 is switched from the passing path T2 to the attenuation path T1. Alternatively, a logic signal for switching from the attenuation path T1 to the passage path T2 is output to the attenuator 23.

  In the above configuration example, the configuration in which the function of the first control unit 101 is realized by analog control has been described, but the function may be realized by digital control.

  Next, the operation of each unit in the automatic gain control device 100 having the above configuration will be described with reference to a block diagram shown in FIG. 11 and a timing diagram of each unit signal shown in FIG.

  The monitoring points A and B of each signal in the automatic gain control device 100 shown in FIG. 11 are the same as the monitoring points A and B of each signal shown in FIG. 2, and each of the monitoring points A and B shown in FIGS. The signal names are the same as those shown in FIGS. It is assumed that the switch SW in the attenuator 23 has been switched to the passing path T2 in the initial state.

  In the automatic gain control device 100 of FIG. 11, when the reception signal of FIG. 12A is input to the input terminal 21, a part thereof is extracted by the input coupler 22 and output to the first control unit 101.

  In the first control unit 101, a change in the DC voltage value obtained by DC-converting the reception signal input from the input coupler 22 is determined by an ascending threshold or a descending threshold set by the comparator 1013 based on the reference voltage value of the reference voltage source 1012. Is compared to In this case, the change in the voltage value of the received signal in FIG. 12A exceeds the ascending threshold value in the upward trend of changing from the low voltage value to the high voltage value. A “High” signal shown in FIG. 12B is output to the attenuator 23 as a logic signal for switching the signal path from the passing path T2 to the attenuation path T1 (output of A in FIG. 11).

  In the attenuator 23, the switch SW is switched from the passing path T2 in the initial state to the attenuation path T1 at the switched timing in FIG. 12B according to the logic signal of FIG. 12B input from the first control unit 101. As a result, the output signal (B in FIG. 11) output from the attenuator 23 is a signal attenuated by the attenuation path T1 as shown in FIG. 12C.

  In the variable gain amplifier 25, when the received signal is input to the automatic gain control device 100, that is, when the switch SW in the attenuator 23 is switched to the passing path T2, the received signal sharply rises, as shown in FIG. The output signal reaches the temporary saturation level as shown in d).

  However, immediately after that, the switch SW in the attenuator 23 is immediately switched to the attenuation path T1 by the operation of the first control unit 101, and the received signal is attenuated. Therefore, the output signal of the variable gain amplifier 25 is as shown in FIG. Is quickly converged to the desired output level shown in FIG.

  Further, as shown in FIG. 12A, when the received signal changes in a variable region, in a region where the voltage value fluctuation is above the descending threshold, the first control unit 101 sends “High” to the attenuator 23. Since the output of the signal is maintained, the output of the attenuator 23 becomes an output signal according to the fluctuation of the received signal in which the DC component has been attenuated, as shown in FIG.

  In the third embodiment, the first controller 101 sets the ascending threshold and the descending threshold, and the switching control of the switch SW in the attenuator 23 has a hysteresis characteristic. The switch SW in the attenuator 23 is appropriately switched between the case where there is a tendency and the case where there is a downward trend to realize gain control according to the voltage value fluctuation of the received signal.

  However, when the first control unit 24 in which only one threshold value is set for the attenuation path is applied in the first embodiment, the reception signal level is reduced as shown by a dashed line in FIGS. The switch SW in the attenuator 23 is switched every time the signal exceeds the threshold value regardless of the rise / fall, and the output of the attenuator 23 becomes an output signal having a waveform different from the fluctuation of the received signal level.

  That is, in the digital communication system, after the preamble signal section included in the received signal ends, communication control information such as a received electric field and data are transmitted. Here, for example, when information transmission is performed using an OFDM modulated wave, a dip point may occur in a received signal when symbol positions of each subcarrier are concentrated in a low amplitude region. At this time, when the first control unit 24 of the first embodiment switches the attenuator 23, the output level of the automatic gain control device 20 becomes unstable.

  Therefore, in the first control unit 101 of the third embodiment, if the level of the dip point is equal to or higher than the descending threshold, the state of the attenuator 23 is maintained, and the automatic gain control device 100 can secure a stable output.

  FIG. 13 is a diagram illustrating an example of an input electric field level and a dynamic range of the automatic gain control device 100 according to the third embodiment.

  In FIG. 13, when the input electric field level is -90 dBm to -20 dBm, in the conventional automatic gain control device, the required dynamic range is 70 dB, and it is necessary to maintain the linearity of the device up to the maximum input level = -20 dBm. is there.

  As described above, according to the automatic gain control device 100 according to the third embodiment, the loss in the passing state of the attenuator 23 is 0 dB, the loss in the attenuation state is 30 dB, the ascending threshold for switching the passing / attenuation state is -50 dBm, and When the threshold value is -60 dBm, the dynamic range of the variable gain amplifier 25 can be reduced to 40 dB and the maximum input level can be reduced to -50 dBm, so that faster gain convergence and a reduction in the noise figure of the entire circuit can be realized. In addition, resistance to a received signal dip can be obtained.

(Embodiment 4)
FIG. 14 is a block diagram showing a configuration of an automatic gain control device 130 according to Embodiment 4 of the present invention. Components identical to those shown in FIG. 1 are given the same reference numerals.

  The feature of the present embodiment is that it has a sample and hold function for switching between discrete switching of the attenuation of the attenuator according to the level fluctuation of the received signal and fixing of the attenuation according to the timing of the signal input from the outside. A first control unit having a sample and hold function for switching between control of the amplification amount of the variable gain amplifier in accordance with the level fluctuation of the received signal and fixing of the amplification amount in accordance with the timing of a signal input from the outside; 2 control units.

  The automatic gain control device 130 mainly includes an input terminal 21, an input coupler 22, an attenuator 23, a first control unit 131, a variable gain amplifier 25, an output coupler 26, a second control unit 132, and an output terminal 28. You. The description of the configuration of the input coupler 22, the attenuator 23, the variable gain amplifier 25, and the output coupler 26 is the same as that of the first embodiment, and thus will be omitted.

  The first control unit 131 includes a detector 1311, a reference voltage source 1312, a comparator 1313, and a sample-and-hold circuit 140. The detector 1311 converts a received signal input from the input coupler 22 into a DC voltage signal. The comparator 1313 compares the DC voltage value with a threshold value based on the reference voltage value of the reference voltage source 1312, and switches the switch SW of the attenuator 23 from the passing path T2 to the attenuation path T1 or from the attenuation path T1 based on the comparison result. The sample-and-hold circuit 140 holds the logic signal to be switched to the passing path T2, and outputs the held logic signal to the attenuator 23.

  The sample and hold circuit 140 includes a switch 141, a capacitor 142, and a high input impedance buffer 143. The switch 141 is on / off controlled by a signal input from an external processing circuit (not shown). Controls the sample and hold period. The sample hold circuit 140 holds the logic signal input from the comparator 1313 and outputs the logic signal to the attenuator 23.

  The second control unit 132 includes a detector 1321, a reference voltage source 1322, an error amplifier 1323, and a sample hold circuit 1324. The detector 1321 converts the amplified reception signal input from the output coupler 26 into a DC voltage signal. The error amplifier 1323 controls the gain of the variable gain amplifier 25 via the sample and hold circuit 1324 so that the DC voltage value matches the reference voltage value of the reference voltage source 1322.

  The internal configuration of the sample and hold circuit 1324 is the same as that of the sample and hold circuit 140, and is not shown. The sample and hold circuit 1324 has its switch on / off controlled by a signal input from an external processing circuit (not shown), and controls a period during which the input signal is sampled and held by the on / off period. The sample hold circuit 1324 holds the gain control signal input from the error amplifier 1323 and outputs the signal to the variable gain amplifier 25.

  In the configuration example described above, the configuration in which the functions of the first control unit 131 and the second control unit 132 are realized by analog control has been described. However, the functions may be realized by digital control.

  In the above configuration example, the second control unit 132 controls the gain of the variable gain amplifier 25 by feeding back the output signal of the variable gain amplifier 25. For example, the second control unit 132 connects the output coupler 26 to the attenuator 23 and the variable gain It may be arranged between the amplifiers 25 to detect the input level of the variable gain amplifier 25 and control the gain of the variable gain amplifier 25 so as to obtain a gain different from a desired output level.

  Next, the operation of each unit in the automatic gain control device 130 having the above configuration will be described with reference to a block diagram shown in FIG. 15 and a timing diagram of each unit signal shown in FIG.

  The monitoring points A and B of each signal in the automatic gain control device 130 shown in FIG. 15 are the same as the monitoring points A and B of each signal shown in FIG. 2, and FIG. 16 (a), (c) to (c). The signal names shown in e) are the same as those shown in FIGS. 3A to 3D. The monitoring point X in FIG. 15 is a monitoring point for monitoring the output of the comparator 1313, and FIG. 16B shows the sample and hold operation of the sample and hold circuits 140 and 1324.

  It is assumed that the switch SW in the attenuator 23 has been switched to the passing path T2 in the initial state, and the switches in the sample hold circuit 140 and the sample hold circuit 1324 have also been turned off.

  In the automatic gain control device 130 of FIG. 15, when the reception signal of FIG. 16A is input to the input terminal 21, a part of the signal is extracted by the input coupler 22 and output to the first control unit 131.

  In the first control unit 131, a DC voltage value obtained by DC-converting the received signal input from the input coupler 22 is compared with a reference voltage value (threshold) of a reference voltage source 1312 by a comparator 1313. In this case, since the voltage value of the received signal in FIG. 16A exceeds the threshold value indicating the reference voltage value, the comparator 1313 determines that the signal path of the attenuator 23 is a logical signal that switches the signal path from the passing path T2 to the attenuation path T1. , A "High" signal shown in FIG.

  At this time, in the sample and hold circuit 140, the switch 141 is turned on by a signal input from an external processing circuit (not shown), and the sample and hold period is set as shown in FIG. This sample hold period is set based on the preamble signal section of the received signal. The sample hold circuit 1324 also performs a sample hold operation.

  As a result of the operation of the sample and hold circuit 140, the “High” signal input from the comparator 1313 to the sample and hold circuit 140 becomes a logical signal (A in FIG. 15) output from the first control unit 131, as shown in FIG. The signal is output to the attenuator 23 as a “High” signal as shown in c).

  In the attenuator 23, the switch SW is switched from the passing path T2 in the initial state to the attenuation path T1 at the switched timing in the drawing by the logic signal input from the first control unit 131. As a result, as the output signal (B in FIG. 15) output from the attenuator 23, a signal attenuated by the attenuation path T1 is output as shown in FIG. 16D.

  In the variable gain amplifier 25, when the reception signal is input to the automatic gain control device 130, that is, in a state where the switch SW in the attenuator 23 is switched to the passing path T2, the reception signal sharply rises, as shown in FIG. As shown in (e), the output signal reaches the temporary saturation level.

  However, immediately after that, since the switch SW in the attenuator 23 is immediately switched to the attenuation path T1 by the operation of the first control unit 131 and the received signal is attenuated, the output signal of the variable gain amplifier 25 is shown in FIG. Is quickly converged to the desired output level shown in FIG.

  When the preamble signal section ends, the sample and hold circuit 140 and the sample and hold circuit 1324 enter a hold state, and the attenuation of the attenuator 23 and the amplification of the variable gain amplifier 25 are fixed, as shown in FIG. Even if a dip occurs below the threshold in the data section of the received signal, the output of the automatic gain controller 130 is kept stable.

  As described above, according to automatic gain control device 130 of the fourth embodiment, even if dip occurs in the data section of the received signal, first control unit 131 and second control unit 132 Since the state and the state of the variable gain amplifier 25 are maintained, a stable output can be secured.

  In the basic operation shown in FIG. 16, the first control unit 131 and the second control unit 132 are controlled at the same timing, but may be controlled at independent timings.

(Embodiment 5)
FIG. 19 is a block diagram showing a configuration of an automatic gain control device 190 according to Embodiment 5 of the present invention, wherein the same components as those shown in FIG. 1 are denoted by the same reference numerals.

  A feature of the present embodiment is that a delay element is arranged between a reception signal level detection unit and a gain switching unit.

  The automatic gain control device 190 includes an input terminal 21, an input coupler 22, a delay element 191, an attenuator 23, a first control unit 24, a variable gain amplifier 25, an output coupler 26, a second control unit 27, and an output terminal 28. Mainly composed. The description of the configuration of the input coupler 22, the attenuator 23, the first control unit 24, the variable gain amplifier 25, the output coupler 26, and the second control unit 27 is omitted because it is the same as in the first embodiment.

  The delay element 191 is an element that delays transmission of a signal for a predetermined time, and can be configured by, for example, a delay line using a coaxial cable, an LC ladder circuit, or the like.

  Next, the operation of each unit in the automatic gain control device 190 having the above configuration will be described with reference to a block diagram shown in FIG. 20 and a timing diagram of each unit signal shown in FIG.

  The monitoring points A and B of each signal in the automatic gain control device 190 shown in FIG. 20 are the same as the monitoring points A and B shown in FIG. 2, and the signal names shown in FIGS. Are the same as those shown in FIGS. 3 (a) to 3 (d). FIG. 21 (c ′) shows the operation state of the output unit (monitoring point C in FIG. 20) of the delay element 191.

  It is assumed that the switch SW in the attenuator 23 has been switched to the passing path T2 in the initial state.

  In the automatic gain control device 190 of FIG. 20, when the reception signal of FIG. 21A is input to the input terminal 21, a part of the signal is taken out by the input coupler 22 and output to the first control unit 24.

  In the first control unit 24, the change in the DC voltage value obtained by DC-converting the received signal input from the input coupler 22 is compared with the reference voltage value (threshold) of the reference voltage source 242 by the comparator 243. In this case, since the voltage value of the received signal in FIG. 21A exceeds the threshold value indicating the reference voltage value, the comparator 243 switches the signal path of the attenuator 23 from the passing path T2 to the attenuation path T1. Here, assuming that the input signal of the attenuator 23 can ignore the delay of the input coupler 22, the received signal of FIG. 21A is delayed by the delay time of the delay element 191 as shown in FIG. Signal. As a result, as shown in FIG. 21C, the output signal output from the attenuator 23 (monitoring point B in FIG. 20) is a signal attenuated by the attenuation path T1 before the reception signal rises. .

  That is, since a signal whose input level is appropriately controlled by the attenuator 23 is input to the variable gain amplifier 25, the output signal of the variable gain amplifier 25 quickly converges to a desired output level shown in FIG. Is done.

  Therefore, according to automatic gain control apparatus 190 of the fifth embodiment, by arranging delay element 191, the gain of the receiving system can be switched before the received signal is transmitted, and the convergence of the gain can be achieved more quickly. A possible automatic gain control device can be provided.

(Embodiment 6)
FIG. 22 is a block diagram showing a configuration of an automatic gain control device 220 according to Embodiment 6 of the present invention, and the same components as those shown in FIG.

  A feature of this embodiment is that the delay element has a frequency selection characteristic.

  The automatic gain control device 220 includes an input terminal 21, an input coupler 22, a delay element 221 having frequency selection characteristics, an attenuator 23, a first control unit 24, a variable gain amplifier 25, an output coupler 26, a second control unit 27, It mainly comprises an output terminal 28. The description of the configuration of the input coupler 21, the attenuator 23, the first control unit 24, the variable gain amplifier 25, the output coupler 26, and the second control unit 27 is omitted because it is the same as that of the first embodiment.

  The delay element 221 is a delay element having frequency selection characteristics, and is configured by, for example, a SAW (Surface Acoustic Wave) filter.

  Next, a receiving circuit 230 to which the automatic gain control device 220 having the above configuration is applied will be described with reference to FIG.

  FIG. 23 shows a configuration example of a receiving circuit 230 to which the automatic gain control device 220 according to the sixth embodiment is applied. Note that, in each component of FIG. 23, a portion corresponding to FIG. 7 is denoted by the same reference numeral.

  In FIG. 23, a receiving circuit 230 includes an antenna 71, a high-frequency band-pass filter 72, a low-noise amplifier 73, a mixer 74, a low-pass filter 75 for suppressing local signals, a first interstage amplifier 76, an input coupler 22, and a frequency selector. It comprises a delay element 221 having characteristics, an attenuator 23, a first control unit 24, a variable gain amplifier 25, an output coupler 26, a second interstage amplifier 78, and a quadrature demodulator 79. It is demodulated to a digital signal by a baseband processor that does not.

  Here, by giving the function of the intermediate frequency band-pass filter 77 in FIG. 7 to the delay element 221 having the frequency selection characteristic, the number of components can be reduced, and the receiving circuit can be realized at lower cost and smaller size.

  An automatic gain control device according to the present invention realizes high linearity and high-speed response in a receiving device of a digital communication system.

FIG. 1 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 1 of the present invention. FIG. 4 is a block diagram for explaining an operation of the automatic gain control device according to the first embodiment when a strong electric field is applied. Timing chart of signals of each part for describing the operation of each part of the automatic gain control device according to the first embodiment when the electric field is strong. Block diagram for explaining operation of the automatic gain control device according to the first embodiment when a weak electric field is applied. Timing charts of signals of respective parts for describing operations of respective parts of the automatic gain control device according to the first embodiment at the time of a weak electric field. Characteristic diagram showing operation characteristics of the automatic gain control device according to the first embodiment and operation characteristics of a conventional automatic gain control device. Block diagram of a receiving circuit to which the automatic gain control device according to the first embodiment is applied. FIG. 4 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 2 of the present invention. Characteristic diagram showing operation characteristics of the automatic gain control device according to the second embodiment and operation characteristics of a conventional automatic gain control device. FIG. 4 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 3 of the present invention. FIG. 9 is a block diagram for explaining an operation of the automatic gain control device according to the third embodiment. Timing charts of signals of respective parts for describing operations of respective parts of the automatic gain control device according to the third embodiment Characteristic diagram showing operation characteristics of the automatic gain control device according to the third embodiment and operation characteristics of a conventional automatic gain control device. 4 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 4 of the present invention. FIG. 10 is a block diagram for explaining an operation of the automatic gain control device according to the fourth embodiment. Timing chart of signals of respective parts for describing operations of respective parts of the automatic gain control device according to the fourth embodiment Block diagram showing the configuration of a conventional automatic gain control device FIG. 1 is a block diagram of a receiving device to which a conventional automatic gain control device is applied, and FIG. FIG. 14 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 5 of the present invention. Block diagram for explaining the operation of the automatic gain control device according to the fifth embodiment. Timing chart of signals of respective parts for describing operations of respective parts of the automatic gain control device according to the fifth embodiment FIG. 14 is a block diagram showing a configuration of an automatic gain control device according to Embodiment 6 of the present invention. Block diagram of a receiving circuit to which the automatic gain control device according to the sixth embodiment is applied.

Explanation of reference numerals

20, 80, 100, 130, 190, 220 Automatic gain control device 21 Input terminal 22 Input coupler 23, 81 Attenuator 24, 82, 101, 131 First control unit 25 Variable gain amplifier 26 Output coupler 27, 132 Second Control unit 28 Output terminal 191, 221 Delay element

Claims (5)

In an automatic gain control device that performs gain control so that the output signal level is constant according to the input received signal level,
Gain switching means for discretely switching the gain for amplifying the received signal,
Gain control means for continuously controlling the gain for amplifying the received signal output by the gain switching means,
A first control unit that detects a reception signal level of an input stage of the gain switching unit and switches the gain of the gain switching unit to a lowering direction when the reception signal level is equal to or more than a predetermined threshold value;
Second control means for controlling the gain of the gain control means so that the output signal level of the gain control means is constant;
An automatic gain control device comprising:   The first control means switches the gain of the gain switching means with a hysteresis characteristic based on different thresholds depending on whether the variation of the received signal level is increasing or decreasing. The automatic gain control device according to claim 1, wherein:   2. The automatic gain control device according to claim 1, wherein the first and second control units switch between gain change and gain fixation by a timing signal input from the outside.   4. The automatic control device according to claim 1, wherein said first control means includes a delay element disposed between a portion for detecting said reception signal level and an input stage of said gain switching means. Gain control device.   5. The automatic gain control device according to claim 4, wherein said delay element has a frequency selection characteristic.

Images